Bug-fix for #119
Bug-fix for #119

Reused switch -t <target_names_sepratade_by_comma> to filter in build names from
build spec. This is case sensitive filter.

Usage:

Run all builds from test specification:

$mbedgt --test-spec ts.json
$mbedgt -VS --test-spec ts.json

Filter in build names by name:

$mbedgt --test-spec ts.json -t K64F-ARM
$mbedgt --test-spec ts.json -t K64F-ARM -n test-case-name1,test-case-name2

ARMmbed/greentea